Purpose/Significance of Application:This application demonstrated that a pilot-scale SVE system removed sufficient vapor contaminants from the vadose zone, and expansion of the system beyond a pilot-scale was not necessary.

Results:- TCE concentrations decreased to less than 1 ppm after 5 months of operation of the SVE system - Rate of TCE extraction decreased from 35 pounds per month to less than 10 pounds per month - Approximately 70 pounds of TCE removed during operation of the system

Description:Soil vapor extraction (SVE) was performed at the Rocky Mountain Arsenal (RMA) Superfund site, Motor Pool Area, in Commerce City, Colorado to remove halogenated volatile organic compounds (VOCs), primarily trichloroethylene, from the vadose zone. The Motor Pool Area at RMA, referred to as Operable Unit 18, had been used for cleaning and servicing equipment, vehicles, and railroad cars, and for storing diesel, gasoline, and oil products in aboveground and underground storage tanks. VOCs, detected in the Motor Pool Area's soil and groundwater have been attributed to releases of chlorinated solvents used during cleaning operations; these solvents were discharged through floor drains and pipes into unlined ditches at the site.

This system was initially considered to be a pilot study because it was expected to provide performance data on SVE at this site that could be used to expand the system to a full-scale operation. This application, operated from July to December 1991, demonstrated that a pilot-scale SVE system removed sufficient vapor contaminants from the vadose zone, and expansion of the system beyond pilot-scale was not necessary. The SVE system used within the Motor Pool Area consisted of one shallow vapor extraction well and one deep vapor extraction well. Four clusters of vapor monitoring wells were installed to aid in the assessment of the performance of the SVE system. TCE levels in soil vapors collected from the vapor monitoring wells were reduced to non-detect or to levels of less than 1 ppm from initial vapor monitoring well samples as high as 65 ppm. Approximately 70 pounds of TCE were recovered during this cleanup action.

The operating parameters collected during the system's 1991 operation indicated that a clay lense located beneath the site affected the SVE system's performance by limiting both the shallow and deep vapor extraction wells' vertical zones of influence. The contract award cost for procuring, installing, and operating the SVE pilot system, as well as preparing a pilot study report was $182,800. This cost was approximately 15% less than the preliminary cost estimate provided by the remediation contractor for the project. Factors contributing to the lower cost included lower construction and system operating costs.